The present invention relates to a method for the detection processing for detecting a candidate of a branched direction and, more particularly, to a method for the detection processing for detecting a candidate of a branched direction, so adapted as to efficiently and accurately perform the detection processing for detecting the candidate of the branched direction for a linear image having a branch in tracing the linear image in an interactive way with an image processing system such as a computer-aided design (CAD) device and the like.
Heretofore, as a method for entering a drawing drawn on paper into a graphics processing system, it is common that the drawing is entered as data of an image through an image scanner or the like, the data of the image is displayed on a display screen through the graphics processing system, and the image is then traced and entered manually with a pointing device or the like, while the operator is looking at the data of the image on the display screen.
For example, Japanese Patent Publication Laid-open (kokai) No. 62-269,276/1987 discloses a graphic input system of an interactive type, which involves entering the drawing into a computer as data of an image through a scanner, displaying the data of the image and data of an image of central lines on the display screen in a superimposed way, and entering the drawing as data of a vector by indicating a necessary position of the drawing on the display screen with a coordinate indicator.
When the data of the image are to be converted into data of a graphic such as the data of the vector as in the manner described hereinabove, for instance, data of centers (central lines) of the image are given, and data on characteristic points of the image, such as terminal points, branched points, corner points and the like, are entered by selecting them from the continuous central line of the data of the centers and indicating them. In this instance, in order to allow the characteristic points to be entered with ease, the data of the centers are superimposed with the data of the image on the display screen in order for the operator to clearly and readily distinguish the characteristic points, and the characteristic points are then entered on the basis of the indication of input by the operator. This system suffers from the disadvantage that the display on the display screen may be made complicated and, as a consequence, an operation for selecting the necessary data by the operator may not be performed with efficiency.
Further, in order that the data of the image are to be converted into the data of the graphic such as the data of the vector, Japanese Patent Publication Laid-open (kokai) No. 60-117,374/1985 proposes a system for approximating polygons of a linear graphic as an example in which data of a linear graphic are given from data of contours of the image without processing for breaking the lines into smaller line sections. This system requires to give the data on the contour lines for all the data of the image in advance when the linear image is converted from the data of the contour lines into the linear graphic.
In addition, an image processing system having a function for the semi-automatic image trace processing has been developed, which is so arranged as to semi-automatically trace points of an image by providing an instruction to trace the data points of the image, to determine the characteristic points, and to enter the data of the graphic for the characteristic points. This function of the semi-automatic image trace processing requires a function for appropriately determining a candidate of a branched direction at a branched point in order to trace the linear image in a correct way.
Furthermore, it can be noted that, for example, when a linear image in the data of the image is subjected to semi-automatic trace processing by giving the instruction to trace the data points of the image--for example, when the semi-automatic image trace processing of the image processing system is applied to the data of the image in a map and the linear image of the image in the map is traced--the data of the image which the operator is required to convert into the data of the graphic include roads, a topographical map, and the like, not symbols, characters, and the like.
In the trace processing, the operator is thus required to determine a traceable direction at a branched point when the trace has reached the branched point, when the function for the semi-automatic image trace processing is employed, which requires the operator to answer to an inquiry about which direction the trace should proceed. The system for approximating the polygons of the linear graphic as proposed hereinabove, however, requires to give data on all the contour lines as pre-processing, even if only one location of a branched point should be investigated. Thus, the prior art system requires a long period of time for useless operations.